With the development of communication technologies, mobile communication systems are developed to be system architecture evolved (SAE) systems.
FIG. 1 illustrates a schematic diagram of an SAE system according to the related art.
Referring to FIG. 1, the system includes an evolved universal terrestrial radio access network (E-UTRAN) 101 and a core network that at least includes a mobility management entity (MME) 105 and a subscriber plane entity (serving gateway (S-GW)) 106. The E-UTRAN 101 is configured to connect a user equipment (UE) to the core network, and the E-UTRAN 101 includes more than one macro base station (evolved Node-B (eNB)) 102 and home base station (home eNB (HeNB)) 103, and optionally includes a home base station gateway (HeNB GW) 104. The MME 105 and the S-GW 106 may be integrated into a module or may be implemented separately and independently. The eNBs 102 are connected with each other by X2 interfaces, and are connected with the MME 105 and S-GW 106 by S1 interfaces respectively. An HeNB 103 is connected with the MME 105 and S-GW 106 directly by S1 interfaces, or is connected with the optional HeNB GW 104 by an S1 interface and then the HeNB GW104 is connected to the MME 105 and the S-GW 106 respectively by an S1 interface.
During an early stage of establishing an SAE system or during the operation of an SAE system, it costs a great amount of manpower and material resource configures to optimize parameters of the SAE system, especially radio parameters, so as to guarantee good coverage and capacity, mobility robustness, load balancing and a user equipment access rate during movement, and the like, of the SAE system. To save manpower and material resource configurations, currently an SAE system self-optimization method is proposed. During a self-optimization procedure, eNB or HeNB settings are optimized according to current status of an SAE system. The SAE system self-optimization method will be illustrated hereafter, and eNB and HeNB are abbreviated to eNB.
FIG. 2 is a flowchart illustrating a basic principle of performing self-optimization for an SAE system according to the related art.
Referring to FIG. 2, once an eNB is powered or accesses to the SAE system, the eNB may perform a self-configuration process. The process includes performing basic configuration and initial radio parameter configuration for the eNB. The basic configuration for the eNB includes configuration of an Internet protocol (IP) address of the eNB and detecting operations, administration, and management (OA&M), validation between the eNB and a core network, detecting an HeNB GW to which the eNB belongs when the eNB is an HeNB, downloading software and operating parameters of the eNB to perform self-configuration. Since the initial radio parameter configuration is implemented according to experience or simulation, thus the performance of respective eNBs of the SAE system will be influenced by environments of areas where the eNBs are located, so the eNBs need to specifically perform initial configuration of a neighbor list and initial configuration of load balance according to the environments of the areas where the eNBs are located. After the self-configuration process is completed, a lot of parameters configured for the eNBs may not be the most optimal, so to make the SAE system having better performance, the configuration of the eNBs needs to be optimized or adjusted, namely self-optimization of a mobile communication system. When the configuration of the eNBs is optimized or adjusted, the process may be carried out through backstage OA&M. There may be a standard interface between the OA&M and an eNB, and the OA&M needs to transmit optimized parameters through the interface to the eNB (may be an eNB or HeNB), then the eNB optimizes parameters of the eNB's configuration according to the optimized parameters. Of course, the process may be performed by the eNB itself. For example, the eNB obtains performance to be optimized by detection, and optimizes or adjusts parameters corresponding thereto. The eNB configuration optimization or adjustment may include: neighbor list self-optimization, coverage and capacity self-optimization, mobility robustness self-optimization, load balancing self-optimization, random access channel (RACH) parameter self-optimization, and the like.
A basic principle of mobility robustness self-optimization is as follows. If a radio link failure (RLF) or handover failure happens to a UE, when the UE enters into connected mode again, the UE notifies the network that there is an available RLF report, and the network transmits a message to the UE to request for the RLF report. The RLF report transmitted by the UE includes information on an E-UTRAN cell global identifier (ECGI) of a cell that serves the UE last, an ECGI of a cell that attempts to be reestablished, an ECGI of a cell that triggers a last handover procedure, time from triggering a last handover procedure to connection failure, a reason for connection failure being RLF or handover failure, radio measurement, and the like. A base station that obtains the RLF report from the UE forwards the RLF report obtained from the UE to a base station where the cell that serves the UE last is located. The base station that serves the UE last determines whether it is a too early handover, a too late handover, a handover to wrong cell, or covering leakage. If it is a too early handover or a handover to wrong cell, the base station transmits information on the too early handover or information on the handover to wrong cell to a source base station that triggers the too early handover or triggers the handover to wrong cell.
For mobility robustness optimization (MRO) between different radio access technologies (RAT), e.g., a too early handover from 3rd generation (3G) or 2nd generation (2G) to long term evolution (LTE), if shortly after a radio network controller (RNC) hands over the UE successfully to eNB1, an RLF happens to the UE at eNB1, when the UE accesses LTE next time, the UE transmits a UE RLF report to an eNB (e.g., eNB2) where the UE accesses LTE a second time, the eNB2 transmits an RLF indication message to the eNB1, and the eNB1 determines a reason for the failure. If it is a too early inter-RAT handover, then the eNB1 needs to transmit a handover report to a source RNC, and since the handover is carried out between different systems, the eNB1 needs to transmit the handover report to the source RNC through a core network. However, during transmission of the handover report, the following issue may occur. According to the RLF indication message transmitted from the eNB2 to the eNB1, the eNB1 only knows a cell identity of a source cell, but the eNB1 would not know other location information of the source cell, which results in that the eNB1 is unable to route the handover report to the source RNC.
Similarly, for transmission of a handover report of an unnecessary handover to another RAT, the issue caused by being unable to transmit the handover report due to not knowing the location information of a source cell of the handover exists too. Specifically, even if the coverage of E-UTRAN is good enough to satisfy requirements for the UE services, the UE still needs to be handed over to another RAT (e.g., global system for mobile communications (GSM) enhanced data rate for GSM evolution (EDGE) radio access network (GERAN), or universal terrestrial radio access network (UTRAN)). Such a handover is an unnecessary handover to another RAT. To detect the unnecessary handover to another RAT, when an inter-RAT handover from the E-UTRAN to another RAT is performed, the eNB needs to contain coverage and quality information in a handover requirement. A radio access network (RAN) node (i.e., RNC or base station sub-system (BSS)) of another RAT indicates the UE to continue to measure the source RAT (i.e., E-UTRAN) for a time. When the time indicated by the source RAT expires, the target RAT (e.g., UTRAN or (GERAN)) decides whether the target RAT needs to transmit an unnecessary inter-RAT handover report to the RAN node of the source RAT. However, currently neither the present RAN node of the RAT knows the information of the source cell, nor does the present RAN node of the RAT know the location information of the source cell. Accordingly, the present RAN node of the RAT cannot transmit the unnecessary inter-RAT handover report to the RAN node of the source RAT.
Further, for MRO between different RATs, the following issues may exist when an RLF report is transmitted. For example, for a too early handover from 3G or 2G to LTE, if shortly after an RNC hands over the UE successfully to eNB1, an RLF happens to the UE at eNB1, when the UE accesses LTE next time, the UE transmits a UE RLF report to an eNB (e.g., eNB2) where the UE accesses LTE a second time, the eNB2 transmits an RLF indication message to the eNB1, and the eNB1 determines the reason for the failure. If it is a too early inter-RAT handover, then the eNB1 needs to transmit a handover report to a source RNC, and since the handover is carried out between different systems, the eNB1 needs to transmit the handover report to the source RNC through a core network. If there is no X2 interface between the eNB1 and the eNB2, then the eNB2 needs to transmit the UE RLF report to the eNB1 via an S1 interface. However, how the eNB2 can know the detailed information of a cell that serves the UE last before the failure happens and how to transmit the UE RLF report to the eNB1 via the S1 interface are issues yet to be addressed in the current specifications.
The source base station and the source RAN node in an embodiment of the present disclosure are of a same concept, including an eNB in LTE, an RNC in UTRAN, or an RAN node BSS in GERAN.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.